Estimating the expected planting area of double- and single-season rice in the Hunan-Jiangxi region of China by 2030

The development of double-season rice cropping systems has made a considerable contribution toward achieving rice self-sufficiency in China. However, the planting area for double-season rice has sharply decreased in the Hunan-Jiangxi region (the most important producing region of double-season rice in China) as a result of the conversion from double- to single-season rice cropping systems (referred as the rice “double-to-single” phenomenon). Due to concerns about the negative effect of the “double-to-single” phenomenon on rice self-sufficiency in China, we have estimated the planting area of double- and single-season rice in the Hunan-Jiangxi region that will be needed by 2030 to maintain the contribution to China’s rice production, based on the most recent 10 years (2011–2020) of historical data available. The results of our analysis can provide guidance for the government’s decision-making when planning the planting area of double- and single-season rice in the Hunan-Jiangxi region.

China is the world's most populous country, with a population of over 1.4 billion people, or 18% of the world human population 1 . However, China has only about 9% of the 1.4 billion hectares of total arable land in the world 2 . The question of "who will feed China?" raised by Dr. Lester R. Brown in 1995 is still worthy of consideration today, and ensuring food security remains a top priority for the Chinese government 3 .
Rice is the staple food on dining-tables of over 65% of the population in China; thus, adequate rice production is critical to ensure food security in China 4 . In order to produce more rice on the limited amount of arable land available, double-season rice cropping systems, which involve successively growing early-season rice (ESR) and late-season rice (LSR) from March to November within a single calendar year, have been extensively developed in southern China 5 . The development of double-season rice cropping systems has made a considerable contribution toward achieving rice self-sufficiency in China 6 .
Hunan and Jiangxi are the top two double-season rice producing provinces in China 7 . However, in recent years, the planting area devoted to double-season rice has sharply decreased in the Hunan-Jiangxi region as a result of the conversion from double-to single-season rice (SSR) cropping systems (referred as the rice "doubleto-single" phenomenon) (Fig. 1A). A reduced rural labor supply and rising labor wages due to urbanization and economic growth are the key driving forces for the rice "double-to-single" phenomenon 11 . Fortunately, the rice "double-to-single" phenomenon has not resulted in a decrease in total rice production in the Hunan-Jiangxi region (Fig. 1B). During the most recent 10 years (2011-2020), the total rice production in the Hunan-Jiangxi region has been ranged from 45.3 to 48.7 million tons (Mt) with an average of 46.6 Mt, and the contribution of the Hunan-Jiangxi region to rice production in China has been maintained at ~ 22%.
Because China's population is still growing 12 , China must continue to increase rice production. The domestic demand for rice grain in China is expected to reach 217 Mt by 2030, when the population of China is expected to stabilize 6 . To meet this demand, the Hunan-Jiangxi region will need to produce 47.7 Mt of rice grains, assuming that the contribution of the Hunan-Jiangxi region to rice production in China remains at the level of the most recent 10 years (~ 22%) (Fig. 1B). This expected rice production (ERP) is 1.1 Mt higher than the average total rice production during the most recent 10 years. In order to avoid the negative effect of the "double-to-single" phenomenon on achieving the ERP in the Hunan-Jiangxi region by 2030, it is necessary to estimate how much planting area of double-season rice will be needed in this region by this point in time. are the estimated grain yields of ESR, LSR, and SSR, respectively; and EPA ESR , EPA LSR , and EPA SSR are the estimated planting areas for ESR, LSR, and SSR, respectively. We assume the following conditions in the Hunan-Jiangxi region by 2030: (1) the total paddy field area will be maintained in the range of 4.57-5.02 million hectares (Mha) that was planted during the years 2011-2020 8,9 ; (2) the ratio of EPA LSR to EPA ESR is the same as the average ratio of planting area of LSR to ESR during 2011-2020 (i.e., 1.07) (Fig. 1A); (3) EPA SSR is the difference between the total paddy field area and the EPA LSR ; and (4) EGY ESR , EGY LSR , and EGY SSR are projected under three scenarios: (1) constant yield scenario, (2) 5% yield increase scenario, and (3) 10% yield increase scenario (Fig. 2). The baseline yield for all three scenarios is the average grain yields during 2011-2020. The EPA ESR , EPA LSR , and EPA SSR in the Hunan-Jiangxi region needed to achieve the expected rice production by 2030 were obtained by solving the above formula and are shown in Fig. 3.
The results presented in Fig. 3 provide guidance and models for the government's decision-making process in the planning planting areas for ESR, LSR, and SSR in the Hunan-Jiangxi region. In brief, farmers will need to plant 2.55-3.   . This finding indicates that it is urgent to avoid a further aggravated "double-to-single" phenomenon while maintaining the total paddy field area in the Hunan-Jiangxi region. Because it is not an easy task to maintain the total paddy field area under the projected scenario for urban expansion 13 , the government should prepare an alternative to reverse the "double-to-single" phenomenon in the Hunan-Jiangxi region. Increasing the mechanized level of farming operation and improving economic returns to farmers are two key aspects for the government to take into account to promote the development of double-season rice. Although the current planting area of double-season rice can fully meet the requirement for achieving the ERP in the Hunan-Jiangxi region by 2030 under both the 5% and 10% yield increase scenarios, there is some difficulty in reaching the yield increase targets. In recent years, the planting area of high-quality rice varieties has been rapidly increased in China 14 . However, grain yield is generally not very high for high-quality rice varieties, although no genetic linkage has been identified between grain yield and quality in rice 15 . Hence, great efforts are required to develop rice varieties with both high quality and high yield. In addition, rice yields are determined not only by the variety but also by environments and crop management practices. Soil nutrient deficiencies, unfavorable climatic conditions (e.g., heat, cold, and drought), and pest infestations have always been major yield-limiting factors for rice production in China 16 . Therefore, great efforts are also required to: (1) improve soil fertility of low-and medium-yielding rice fields and optimize nutrient management practices; (2) develop climate-smart agriculture practices for alleviating climatic stresses; and (3) promote integrated pest management practices.

Data availability
All data generated or analysed during this work are included in the article.